We have been successfully writing to NFC tags using Beta 13, but have had no luck with trying to lock them using the writeLock() function. After execution we get back a result of nil but it is definitely not locking. Any clues or has anyone managed to get this work as yet?
Code is extremely straight forward (but might have done something stupid!) - Trying on different variations of a NXP NTAG213 tag:
if (self.lockTag) {
// locking required also
os_log("Tag needs to be locked")
tag.writeLock() { (error: Error?) in
if error != nil {
os_log("LOCK FAILED!!")
session.alertMessage = "Lock failed try again"
session.invalidate()
} else {
session.alertMessage = "Write and Lock successful"
session.invalidate()
}
}
} else {
// only writing
os_log("Tag is unlocked")
session.alertMessage = "Write successful!"
session.invalidate()
}
Yes - I was being stupid and missed out the some returns. This codes works perfectly and locks NFC tags:
if (self.lockTag) {
// locking required also
os_log("Tag needs to be locked")
tag.writeLock() { (error: Error?) in
if error != nil {
os_log("LOCK FAILED!!")
session.alertMessage = "Lock failed try again"
session.invalidate()
return
} else {
session.alertMessage = "Write and Lock successful"
session.invalidate()
return
}
}
return
Related
obviously I am new to RxSwift and though I consumed a lot of documentations and speeches, I think I am missing some fundamental concepts.
In my app I have a RESTful web service to load various resources but the base url of the web service is unknown at build/start time. Instead I have a "URL resolver" web service which I can call with my apps bundle, version and possible environment ("production", "debug" or any custom string entered in the apps debug settings) to obtain the base url I then use for the actual service.
My thinking was that I would create 2 services, one for the URL resolver and one for the actual web service which gives me my resources. The URL resolver would have a Variable and a Observable. I use the variable to signal the need to refresh the base url via a web service call to the URL resolver. I do this by observing the variable and filter only for true values. A function in the service class set the variables value to true (initially it is false) and inside an observer of the filtered variable, I make the web service call in another Observable (this example uses a dummy JSON web service):
import Foundation
import RxSwift
import Alamofire
struct BaseURL: Codable {
let title: String
}
struct URLService {
private static var counter = 0
private static let urlVariable: Variable<Bool> = Variable(false)
static let urlObservable: Observable<BaseURL> = urlVariable.asObservable()
.filter { counter += 1; return $0 }
.flatMap { _ in
return Observable.create { observer in
let url = counter < 5 ? "https://jsonplaceholder.typicode.com/posts" : ""
let requestReference = Alamofire.request(url).responseJSON { response in
do {
let items = try JSONDecoder().decode([BaseURL].self, from: response.data!)
observer.onNext(items[0])
} catch {
observer.onError(error)
}
}
return Disposables.create() {
requestReference.cancel()
}
}
}
static func getBaseUrl() {
urlVariable.value = true;
}
static func reset() {
counter = 0;
}
}
Now the problem is that sometimes it can happen that a web service call fails and I would need to show the error to the user so a retry can be made. I thought that the onError was useful for this but it seems to kills all the subscribers forever.
I could put the subscribing in its own function and inside the error handler of the Observer, I could show a alert and then call the subscribe function again like so:
func subscribe() {
URLService.urlObservable.subscribe(onNext: { (baseURL) in
let alert = UIAlertController(title: "Success in Web Service", message: "Base URL is \(baseURL.title)", preferredStyle: .alert)
let actionYes = UIAlertAction(title: "Try again!", style: .default, handler: { action in
URLService.getBaseUrl()
})
alert.addAction(actionYes)
DispatchQueue.main.async {
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alert, animated: true, completion: nil)
}
}, onError: { error in
let alert = UIAlertController(title: "Error in Web Service", message: "Something went wrong: \(error.localizedDescription)", preferredStyle: .alert)
let actionYes = UIAlertAction(title: "Yes", style: .default, handler: { action in
URLService.reset()
self.subscribe()
})
alert.addAction(actionYes)
DispatchQueue.main.async {
VesselService.reset()
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alert, animated: true, completion: nil)
}
}).disposed(by: disposeBag)
}
Then in my AppDelegate I would call
subscribe()
URLService.getBaseUrl()
The problem is that all other observers get killed on an error as well but since the the only other observer on the URLService.urlObservable is my other web service class, I guess I could implement the same style subscribe function in there as well.
I read that some people suggest to return a Result enum which has 2 cases: the actual result (.success(result: T)) or an error (.error(error: Error)).
So what is the better way of handling errors web service errors in Rx? I cant wrap my head around this problem and I'm trying for 2 days to understand it. Any ideas or suggestions?
Update
It just came to my mind that I could ignore errors from the web service calls completely and instead post any error to a global "error" variable which my app delegate could observe to show alerts. The "error" could reference the function which initially caused it so a retry could be made. I'm still confused and not sure what I should do. :/
Update 2
I think I might found a working solution. As I am still a beginner to Rx and RxSwift, I'm happy to take improvement suggestions. As I was writing the actual code, I splitted my call chain in two parts:
The part where I make the web service calls
The part where I click a button and process the result of the web service, whether it is an error or a success
In the part where I click the button and process the result, I use catchError and retry as suggested in the comments. The code looks like this:
let userObservable = URLService
.getBaseUrl(environment: UserDefaults.standard.environment) //Get base url from web service 1
.flatMap({ [unowned self] baseURL -> Observable<User> in
UserService.getUser(baseURL: baseURL,
email: self.usernameTextField.text!,
password: self.passwordTextField.text!) //Get user from web service 2 using the base url from webservice 1
})
signInButton
.rx
.tap
.throttle(0.5, scheduler: MainScheduler.instance)
.flatMap({ [unowned self] () -> Observable<()> in
Observable.create { observable in
let hud = MBProgressHUD.present(withTitle: "Signing in...");
self.hud = hud
observable.onNext(())
return Disposables.create {
hud?.dismiss()
}
}
})
.flatMap({ () -> Observable<User> in
return userObservable
})
.catchError({ [unowned self] error -> Observable<User> in
self.hud?.dismiss()
self.handleError(error)
return userObservable
})
.retry()
.subscribe(onNext: { [unowned self] (user) in
UserDefaults.standard.accessToken = user.accessToken
UserDefaults.standard.tokenType = user.tokenType
self.hud?.dismiss()
})
.disposed(by: disposeBag)
The trick was to move the call to the two web services out of the cain into their own variable so I can re-call it at any time. When I now return the "userObservable" and an error happens during the web service call, I can show the error in the catchError and return the same "userObservable" for the next retry.
At the moment this only properly handles errors when they occur in the web service call chain so I think I should make the button tap a driver.
Okay so for everyone who comes here, you probably have a lack of understanding or a misconception of how the Rx world is supposed to work. I still find it sometimes confusing but I found a way better solution than what I posted in my original question.
In Rx, a error "kills" or rather completes all observers in the chain and that is actually a good thing. If there are expected errors like API error in web service calls, you should either try to handle them where they occur or treat them like expected values.
For example, your observer could return a optional type and subscribers could filter for the existence of values. If an error in the API call occurs, return nil. Other "error handlers" could filter for nil values to display error messages to the user.
Also viable is to return a Result enum with two cases: .success(value: T) and .error(error: Error). You treat the error as a acceptable result and the observer is responsible for checking if it should display a error message or the success result value.
Yet another option, which surely is not the best as well but works it to simply nest the call which you expect to fail inside the subscriber of the call which must not be affected. In my case that is a button tap which causes a call to a web service.
The "Update 2" of my original post would become:
signInButton.rx.tap.throttle(0.5, scheduler: MainScheduler.instance)
.subscribe(onNext: { [unowned self] () in
log.debug("Trying to sign user in. Presenting HUD")
self.hud = MBProgressHUD.present(withTitle: "Signing in...");
self.viewModel.signIn()
.subscribe(onNext: { [unowned self] user in
log.debug("User signed in successfully. Dismissing HUD")
self.hud?.dismiss()
}, onError: { [unowned self] error in
log.error("Failed to sign user in. Dismissing HUD and presenting error: \(error)")
self.hud?.dismiss()
self.handleError(error)
}).disposed(by: self.disposeBag)
}).disposed(by: self.disposeBag)
The MVVM view model makes the calls to the web serivces like so:
func signIn() -> Observable<User> {
log.debug("HUD presented. Loading BaseURL to sign in User")
return URLService.getBaseUrl(environment: UserDefaults.standard.environment)
.flatMap { [unowned self] baseURL -> Observable<BaseURL> in
log.debug("BaseURL loaded. Checking if special env is used.")
if let specialEnv = baseURL.users[self.username.value] {
log.debug("Special env is used. Reloading BaseURL")
UserDefaults.standard.environment = specialEnv
return URLService.getBaseUrl(environment: specialEnv)
} else {
log.debug("Current env is used. Returning BaseURL")
return Observable.just(baseURL)
}
}
.flatMap { [unowned self] baseURL -> Observable<User> in
log.debug("BaseURL to use is: \(baseURL.url). Now signing in User.")
let getUser = UserService.getUser(baseURL: baseURL.url, email: self.username.value, password: self.password.value).share()
getUser.subscribe(onError: { error in
UserDefaults.standard.environment = nil
}).disposed(by: self.disposeBag)
return getUser
}
.map{ user in
UserDefaults.standard.accessToken = user.accessToken
UserDefaults.standard.tokenType = user.tokenType
return user
}
}
First I was thinking to only call the view models signIn() function when pressing the button but since there should be no UI code in the view model, I figured that presenting and dismissing the HUD is the responsibility of the ViewController.
I think this design is now pretty solid. The button observer never completes and can continue to send events forever. Earlier, if there was a second error, it might happen that the button observer died and my logs showed that the userObservable was executed twice, which must also not be happen.
I just wonder if there is a better way then nesting the subscribers.
Important Fact
I forgot to mention an important factor in the question. I am running this in a TestCase. I think this issue has something to do with the TestCase not awaiting for async completionHandler to return
Migrated out from Alamofire to SwiftHTTP, since I found this much easier.
On SwiftHHTP there is no way to know what URL got generated, what error it returned. For example, I tried to see the opt.debugDescription variable, it returned something cryptic like description String "<SwiftHTTP.HTTP: 0x60000007e540>"
Steps I have followed
I have set YES to Allow Arbitrary Loads.
Safari on the iPhone Simulator responds with the correct JSON if I paste fullurl ->http://120.0.0.1:8080/myapi/Driver/getDriver?driver=2243&domain=4345&key=asdfasdf. Even catalina.out on the tomcat server running on my mac responds with a debug message.
But when I run this in a test case under Xcode the below code prints none of debug print's.
--1->, --2-->, --3-->, nothing got printed.
Debugger breakpoints also dont stop here.
CODE
var getData = [String:String]()
getData = ["domain": "4345",
"driver" : "2343",
"key" : "asdfasdf"]
var urlComponents = URLComponents(string: fullURL)!
var queryItems = [URLQueryItem]()
queryItems = self.getData.map{ URLQueryItem(name : $0.0, value : $0.1) }
urlComponents.queryItems = queryItems
print("fullurl ->"+(urlComponents.url)!.absoluteString)
do {
let opt = try HTTP.GET((urlComponents.url)!.absoluteString)
opt.start { response in
if let err = response.error {
print("--1-> error: \(err.localizedDescription)")
return //also notify app of failure as needed
}
print("--2--> opt finished: \(response.description)")
self.responseData = response
}
} catch let error {
print("--3--> got an error creating the request: \(error)")
}
EDIT
Even after changing the code to https or http://www.google.com, same result.
let testComponents = URLComponents(string: "https://www.google.com")!
URLSession.shared.dataTask(with: (testComponents.url)!, completionHandler: {
(data, response, error) in
if(error != nil){
print("..1>..")
}else{
do{
print ("..2>.." )
let json = try JSONSerialization.jsonObject(with: data!, options:.allowFragments) as! [String : AnyObject]
self.responseData = json
}catch let error as NSError{
print("..3>..")
}
}
}).resume()
EDIT 1
Tried from here #Vivek's answer.
callWebService(url: (urlComponents.url)!.absoluteString)
.
.
func callWebService(url : String) {
.
.
let callURL = URL.init(string: url)
Nothing got printed again, Error / JSON, nothing.
Yes, Unit Tests don't wait by default for the completionHandler to be called. If you call asynchronous functions in tests, you don't need to change the function's code, but the behavior of the test.
The solution: XCTestExpectation
In your test-class (the subclass of XCTest), add this property:
var expectation: XCTestExpectation?
A test-function for an asynchronous request could basically look like this:
func testRequest() {
expectation = expectation(description: "Fetched sites") //1
//2
some.asyncStuffWithCompletionHandler() {
someData in
if someData == nil {
XCTestFail("no data") //3
return
}
//looks like the request was successful
expectation?.fulfill() //4
}
//5
waitForExpectations(timeout: 30, handler: nil)
}
Explanation
This defines, what you expect the tested code to do. But actually, it's not important, what you add as description. It's just an information for you, when running the test
This is the function with a completionHandler, you are calling
If you want to let the test fail within the completionHanlder, call XCTestFail()
If everything in the completionHandler worked as expected, fulfill the expectation by calling expectation?.fulfill.
Here comes the important part: This part of the code will be executed before the completionHandler! If this would be the end of the function, the test would be stopped. That's why we tell the test to wait until the expectations are fulfilled (or a certain amount of time passed)
There is an interesting blog post about Unit Tests. (see the section "XCTestExpectation") It's written in an old Swift syntax, but the concept is the same.
I'm working on SkylinkJS for IOS version. On website, it's good. Everything runs correctly. But on IOS, I write the app by Swift.
Everything is good too except the app just crash sometime while trying to disconnect from the room. And I know for sure this error is from the room disconnection. Because If I just go to that viewcontroller and don't connect to any room or just connect to that room and leave without disconnection. Everything will be ok.
The error is:
2017-01-09 13:51:49.187237 Star Dial[8187:3318041] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[1]'
*** First throw call stack:
(0x1834c11b8 0x181ef855c 0x1833a4eac 0x1833a4d1c 0x1001bba70 0x102689218 0x102695a90 0x1001b7ee4 0x102689258 0x102689218 0x102696aec 0x10268cce0 0x102697088 0x102698e2c 0x102698b78 0x1825532a0 0x182552d8c)
libc++abi.dylib: terminating with uncaught exception of type NSException
The code from button disconnect:
if self.skylinkConn != nil {
self.skylinkConn?.disconnect({
print(">>> PROFILE DISCONNECTED")
if profile_before == "home" {
profile_before = ""
self.dismiss(animated: true, completion: nil)
} else if profile_before == "following" || profile_before == "follower" {
profile_before = ""
self.dismiss(animated: true, completion: nil)
} else {
profile_before = ""
let storyBoard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let next = storyBoard.instantiateViewController(withIdentifier: "HomeView") as! HomeController
self.present(next, animated: true, completion: nil)
}
})
}
profile_before is from root class. So it's not the reason. The weird thing is that this error only happens sometime... like when I open this controller 30, 40 times, it will be crash one time... and sometime, I open this page about 100 times and crash.
And for sure, it's not because of the memories too. I check the memory, average during that time is 20-30 MB
I am working in the Temasys Engineering team. The described issue has been resolved. If anyone encounter the problem again please make sure the Temasys SDK for iOS is up to date.
Looks like my node server dies in parseJSON.
Looked at the logs and the last message was "before parse" and it never printed "after parse". What's strange is that I wrapped JSON.pars with try-catch so I am not sure how it caused the server crashed. Any thoughts?
logger.print("before parse")
parseJSON(data)
logger.print("after parse")
and I have pareJSON catch exception.
function parseJSON(str) {
try {
var result = JSON.parse(str);
return result;
} catch (err) {
return null
}
}
If your code crashes in parseJSON then I would try:
try {
logger.print("before parse")
parseJSON(data)
logger.print("after parse")
} catch (e) {
console.log(e);
}
It is strange because your function should catch the exception but this would show what happens. I would also add:
console.log(data.length);
to see the size of the data.
Also I wrote a module tryjson that parses JSON without throwing exceptions. You can try using it but if your function crashes then maybe my module would not handle it either. Though I'd love to know what actually happens.
i have a kohana site and i want to put it into production, but i have a problem i don't know how to solve best:
if someone accesses a uri that doesn't exist, relatively to my website, an error page appears, with the header message:
Kohana_Request_Exception [ 0 ]: Unable
to find a route to match the URI: (and the uri here)
i wonder if I can do something to redirect the user to a standard 404 page, when he/she accesses such a URI,can I?
thank you very much!
You can wrap your $request->execute() in your APPPATH/bootstrap.php with a try/catch block and then do whatever you want.
Mine looks like this...
try
{
// Attempt to execute the response
$request->execute();
}
catch (Kohana_Request_Exception $e)
{
if (Kohana::$environment === Kohana::DEVELOPMENT) throw $e;
// Log the error
Kohana::$log->add(Kohana::ERROR, Kohana::exception_text($e));
// Create a 404 response
$request->status = 404;
$request->response = Request::factory('errors/404')->execute();
}
catch (Exception $e)
{
if (Kohana::$environment === Kohana::DEVELOPMENT) throw $e;
// Log the error
Kohana::$log->add(Kohana::ERROR, Kohana::exception_text($e));
// Create a 500 response
$request->status = 500;
$request->response = Request::factory('errors/500')->execute();
}
Ideally PHP would support finally { ... } and I could do the logging and possible re-throwing there, but what can you do?
You can handle all errors the same way it is described in the userguide for http exceptions:
http://kohanaframework.org/3.1/guide/kohana/errors#http-exception-handling
Try out this one
define('IN_PRODUCTION', TRUE);
// Instantiate your Request object
$request = Request::instance();
try
{
$request->execute();
}
catch (Exception $e) // if its not valid, it gets caught here
{
if (! IN_PRODUCTION) // if this is Development, its displays the error
{
throw $e;
}
// if its IN_PRODUCTION, it does the following:
// Logs the error
Kohana::$log->add(Kohana::ERROR, Kohana::exception_text($e));
// Marks the status as 404
$request->status = 404;
$request->response = $request->factory('sitemap')->execute();
}
// then continues on with the request process to display your custom 404 page
$request->send_headers()->response;
echo $request->response;